Vectors

At 2pm the coastguard spots a dinghy 500m due south of his observation point. The dingy has constant velocity (2i + 3j)ms^-1.

a) Find in terms of t, the position vector of the dinghy t seconds after 2 seconds.
b) Find the distance of the dinghy from the observation point at 2:05pm

I can do a) however im struggling with b) ................. i'll quickly run through a) so it will help with answer b)

a) -500j + (2i + 3j)t = 2ti + (3t-500)j

help with b) would be much appreciated